1. Field of the Invention
The present invention relates to a continuously variable, conical disk transmission with an integrated torque sensor. More particularly, the present invention relates to a continuously variable, conical disk transmission with an integrated torque sensor for controlling the contact pressure between the conical disks and an endless, torque-transmitting member that passes between two pairs of conical disks.
2. Description of the Related Art
A transmission of the type herein disclosed is described in German Patent Publication DE 199 519 50 A1 and will be explained in greater detail below with the help of FIG. 4, which shows a longitudinal section through parts of the transmission and shows its hydraulic control.
An input shaft 6, which is connected with an internal combustion engine by way of a starting clutch, for example, drives a hydraulic pump 8. The pump can be connected through a spool valve 10 with either a return 12 or, alternatively, with a conduit 14 that can be connected to an adjusting chamber, further described below, for adjusting a conical disk 4. A pressure relief valve 15 is arranged between the pump 8 and the spool valve 10. Pump 8 is connected by another line 16 to a pressure chamber that is further described below and that determines the contact pressure with which the conical disks 2 and 4 contact a loop member 18 that can be in the form of a chain. An adjustable conical disk of another pair of conical disks (not shown) has a corresponding pressure chamber that is also supplied with pressure through conduit 16.
The basic function of such a conical disk transmission mechanism, shown in the upper half of FIG. 4 at maximum conical disk spacing and in the lower half at minimum conical disk spacing, is known and will therefore not be described herein.
A generally conical seal support 20 is rigidly connected with the free end of a hollow shaft 5 that is integrally formed with the non-adjustable conical disk 2, and terminates in a cylindrical region 22. A fixed annular element 25 that is tightly connected with conical disk 4 is movable on a radially-outwardly-facing surface of seal support 20, between which an annular seal 24 is arranged. An annular sleeve 28 of conical disk 4 is sealingly guided on a radially-inwardly-facing cylindrical surface 26 of seal support 20, between which an annular seal is arranged.
Arms 32 (for example, three arms) that are distributed in a circumferential direction and that are rigidly connected to a sensing piston 34, extend through openings 30 or pockets in the conical region of seal support 20. At its radial inner end, sensing piston 34, which is generally cup-shaped, is axially movable on the outer periphery of hollow shaft 5. A cylindrical region extends from the radially-extending base of sensing piston 34, the outer surface of which is movably guided, and tightly engages a radially-inwardly facing surface of an annular ring 36 of seal carrier 20, between which an annular seal is arranged. The right front surface of annular ring 36, as viewed in FIG. 4, is formed as an approximately radially extending cam surface 38 that has a curved peripheral surface, opposite from which is positioned a further, approximately radially-extending cam surface 40 that has a curved peripheral surface, and that is carried on a curved extension 41 of the free end of sensing piston 34.
Cam surfaces 38 and 40 receive between them balls 42 that serve as rolling bodies and that determine the axial position of sensing piston 34.
For guiding balls 42, a concave guide surface 46 is formed on the outer side of an annular extension 44 on movable conical disk 4, that corresponds to a similarly concave and generally obliquely-extending guide surface 48 that is angled at its end, and that is formed on a sheet metal element 50 that is rigidly connected with conical disk 4.
Arms 32, which are formed as sheet metal parts, extend into an annular element 33 at their radially-outwardly-directed ends, and that is formed with a slide tooth system that meshes with a corresponding slide tooth system on a sleeve. The sleeve mates with the gears of an intermediate transmission assembly 54 that, in turn, is in meshing engagement with the rotationally driven drive shaft 6. Depending upon the operation of one of two clutches 55, the direction of rotation of conical disks 2 and 4 changes.
Two pressure chambers are formed between seal carrier 20 and conical disk 4xe2x80x94a radially inner contact pressure chamber 56 and a radially outer adjustment chamber 58. Adjustment chamber 58 is supplied with hydraulic medium from conduit 14 by way of bores formed in seal carrier 20 and a blind bore in drive shaft 6. Contact pressure chamber 56 is supplied with hydraulic medium pressure through an axial blind bore 60 in drive shaft 6 and radial bores. A radial bore serving as a return opening 62, is supplied with the pressure within contact pressure chamber 56 from within the annular ring 36, and is more or less widely pre-closed by sensing piston 34, and opens into a further axial blind bore in drive shaft 6.
The function of the torque sensor that is constituted by balls 42, annular ring 36, and sensing piston 34, all arranged together within contact pressure chamber 56, is as follows:
If only a weak torque is provided by drive shaft 6 and if sensing piston 34 is correspondingly loaded with only a weak torque by arms 32, the piston is found to be in its leftmost position, as viewed in FIG. 4, whereby the radial bore serving as a return opening 62 is substantially unblocked by sensing piston 34, so that the pressure in contact pressure chamber 56 is low.
If the torque increases, sensing piston 34 has the tendency to twist relative to conical disk 4 or relative to sheet metal component 50, whereby the sensing piston will shift toward the right due to the influence of balls 42 as they roll on the cam surfaces, thereby increasingly closing return opening 62, so that the pressure in contact pressure chamber 56 increases. In that way, the contact pressure of conical disks 2 and 4 against loop member 18 depends upon the torque.
At constant torque, by appropriate admission of hydraulic medium into adjustment chamber 58 there results an adjustment of conical disk 4 to the right (toward lower speed ratios or the speed of the conical disk transmission; loop member 18 thereby travels toward the outside), and thus balls 42 are shifted radially inwardly by guide surfaces 46 and 48. Because of the radially changing slope of cam surfaces 38 and 40 in the direction of the periphery, the pressure in contact pressure chamber 56 decreases.
From the above it is apparent that the contact pressure that acts on loop member 18 between conical disks 2 and 4 depends not only on the torque applied through the intermediate gear set 54, but also on the distance between the conical disks, and thereon depends the speed ratio of the transmission. That is adjusted in terms of a contact pressure that is sufficient for the given operating conditions but as low as possible, and that ensures a slip-free run of loop member 18 between conical disks 2 and 4, whereby the energy consumption is reduced and the life span is increased.
A characteristic of the above-described transmission consists in that balls 42 influence the prevailing pressure in the contact pressure chamber, corresponding to the speed of the transmission, and thereby the centrifugal force that acts on them, because they attempt to move radially outwardly along guide surfaces 46 and 48 as the rotational speed increases, and thereby exert an additional adjusting force on cam surface 40 of sensing piston 34. That results in an undesired speed dependence of the contact pressure. Furthermore, the movement of the balls along the guide surfaces is accompanied with distinct friction, which, depending upon the adjustment direction and the adjustment speed of the transmission ratio, causes an increase or decrease of the contact pressure, leading to undesired hysteresis.
The present invention is directed to providing a solution for the above-mentioned problem and to improving a belt-driven, conical pulley transmission of that type, so that the influence of centrifugal force on the contact pressure and the hysteresis characteristics is reduced.
That objective is achieved in accordance with the present invention.
In accordance with the invention, the ramps that are provided on the guide surfaces achieve, on one hand, that the movement of the balls along the guide surfaces depends less on direction, which reduces hysteresis. Furthermore, the ramps are formed in coordination with the cam surfaces in such a way as to reduce or to completely eliminate the influence of centrifugal force on the adjusting force that acts on the sensing piston, and thereby the contact pressure.